Adolescence
Adolescence (from Latin adolescere, meaning 'to grow up')1 is a transitional stage of physical and psychological development that generally occurs during the period from puberty to legal adulthood (age of majority).123Adolescence is usually associated with the pre-teen and teenage years,3456 but its physical, psychological or cultural expressions may begin earlier and end later. For example, puberty now typically begins during preadolescence, particularly in females.478910 Physical growth (particularly in males), and cognitive development can extend into the early twenties. Thus age provides only a rough marker of adolescence, and scholars have found it difficult to agree upon a precise definition of adolescence.781112 A thorough understanding of adolescence in society depends on information from various perspectives, including psychology, biology, history, sociology, education, and anthropology. Within all of these perspectives, adolescence is viewed as a transitional period between childhood and adulthood, whose cultural purpose is the preparation of children for adult roles.13 It is a period of multiple transitions involving education, training, employment and unemployment, as well as transitions from one living circumstance to another.14 The end of adolescence and the beginning of adulthood varies by country and by function. Furthermore, even within a single nation state or culture there can be different ages at which an individual is considered (chronologically and legally) mature enough for society to entrust them with certain privileges and responsibilities. Such milestones include driving a vehicle, having legal sexual relations, serving in the armed forces or on a jury, purchasing and drinking alcohol, voting, entering into contracts, finishing certain levels of education, and marriage. Adolescence is usually accompanied by an increased independence allowed by the parents or legal guardians, including less supervision as compared to preadolescence. In studying adolescent development,15 adolescence can be defined biologically, as the physical transition marked by the onset of puberty and the termination of physical growth; cognitively, as changes in the ability to think abstractly and multi-dimensionally; or socially, as a period of preparation for adult roles. Major pubertal and biological changes include changes to the sex organs, height, weight, and muscle mass, as well as major changes in brain structure and organization. Cognitive advances encompass both increment in knowledge and in the ability to think abstractly and to reason more effectively. The study of adolescent development often involves interdisciplinary collaborations. For example, researchers in neuroscience or bio-behavioral health might focus on pubertal changes in brain structure and its effects on cognition or social relations. Sociologists interested in adolescence might focus on the acquisition of social roles (e.g., worker or romantic partner) and how this varies across cultures or social conditions.16 Developmental psychologists might focus on changes in relations with parents and peers as a function of school structure and pubertal status.17 Some scientists have questioned the universality of adolescence as a developmental phase, arguing that traits often considered typical of adolescents are not in fact inherent to the teenage years. Puberty is a period of several years in which rapid physical growth and psychological changes occur, culminating in sexual maturity. The average age of onset of puberty is at 11 for girls and 12 for boys.1819 Every person's individual timetable for puberty is influenced primarily by heredity, although environmental factors, such as diet and exercise, also exert some influences.2021 These factors can also contribute to precocious and delayed puberty.1221 Some of the most significant parts of pubertal development involve distinctive physiological changes in individuals' height, weight, body composition, and circulatory and respiratory systems.22 These changes are largely influenced by hormonal activity. Hormones play an organizational role, priming the body to behave in a certain way once puberty begins,23 and an active role, referring to changes in hormones during adolescence that trigger behavioral and physical changes.24 Puberty occurs through a long process and begins with a surge in hormone production, which in turn causes a number of physical changes. It is the stage of life characterized by the appearance and development of secondary sex characteristics (for example, a deeper voice and larger adam's apple in boys, and development of breasts and more curved and prominent hips in girls) and a strong shift in hormonal balance towards an adult state. This is triggered by the pituitary gland, which secretes a surge of hormonal agents into the blood stream, initiating a chain reaction to occur. The male and female gonads are subsequently activated, which puts them into a state of rapid growth and development; the triggered gonads now commence the mass production of the necessary chemicals. The testes primarily release testosterone, and the ovaries predominantly dispense estrogen. The production of these hormones increases gradually until sexual maturation is met. Some boys may develop gynecomastia due to an imbalance of sex hormones, tissue responsiveness or obesity. Facial hair in males normally appears in a specific order during puberty: The first facial hair to appear tends to similar with adult and grow at the corners of the upper lip, typically between 10 and 17 years of age.2627 It then spreads to form a moustache over the entire upper lip. This is followed by the appearance of hair on the upper part of the cheeks, and the area under the lower lip.26 The hair eventually spreads to the sides and lower border of the chin, and the rest of the lower face to form a full beard.26 As with most human biological processes, this specific order may vary among some individuals. Facial hair is often present in late adolescence, around ages 17 and 18, but may not appear until significantly later.2728 Some men do not develop full facial hair for 10 years after puberty.27 Facial hair continues to get coarser, darker and thicker for another 2–4 years after puberty.27 The major landmark of puberty for males is spermarche, the first ejaculation, which occurs, on average, at age 13.29 For females, it is menarche, the onset of menstruation, which occurs, on average, between ages 12 and 13.20303132 The age of menarche is influenced by heredity, but a girl's diet and lifestyle contribute as well.20 Regardless of genes, a girl must have a certain proportion of body fat to attain menarche.20 Consequently, girls who have a high-fat diet and who are not physically active begin menstruating earlier, on average, than girls whose diet contains less fat and whose activities involve fat reducing exercise (e.g. ballet and gymnastics).2021 Girls who experience malnutrition or are in societies in which children are expected to perform physical labor also begin menstruating at later ages.20 The timing of puberty can have important psychological and social consequences. Early maturing boys are usually taller and stronger than their friends.33 They have the advantage in capturing the attention of potential partners and in becoming hand-picked for sports. Pubescent boys often tend to have a good body image, are more confident, secure, and more independent.34 Late maturing boys can be less confident because of poor body image when comparing themselves to already developed friends and peers. However, early puberty is not always positive for boys; early sexual maturation in boys can be accompanied by increased aggressiveness due to the surge of hormones that affect them.34 Because they appear older than their peers, pubescent boys may face increased social pressure to conform to adult norms; society may view them as more emotionally advanced, despite the fact that their cognitive and social development may lag behind their appearance.34 Studies have shown that early maturing boys are more likely to be sexually active and are more likely to participate in risky behaviors.35 For girls, early maturation can sometimes lead to increased self-consciousness, though a typical aspect in maturing females.36 Because of their bodies' developing in advance, pubescent girls can become more insecure and dependent.36 Consequently, girls that reach sexual maturation early are more likely than their peers to develop eating disorders (such as anorexia nervosa). Nearly half of all American high school girls' diets are to lose weight.36 In addition, girls may have to deal with sexual advances from older boys before they are emotionally and mentally mature.37 In addition to having earlier sexual experiences and more unwanted pregnancies than late maturing girls, early maturing girls are more exposed to alcohol and drug abuse.38 Those who have had such experiences tend to perform not as well in school as their "inexperienced" peers.39 Girls have usually reached full physical development around ages 15–17,31940 while boys usually complete puberty around ages 16–17.194041 Any increase in height beyond the post-pubertal age is uncommon. Girls attain reproductive maturity about four years after the first physical changes of puberty appear.3 In contrast, boys accelerate more slowly but continue to grow for about six years after the first visible pubertal changes.3441